标识符是否符合要求判定

import keyword
import string
alp = string.letters +'_'
nums = string.digits
print "welcome to identifier check v1.0."
print "you have to enter two char to identifier."
keywords= keyword.kwlist
myinput =raw_input(">")
if myinput[0] not in alp:
    print "invalid:first symbol must be alphabetic"
else :
    if len(myinput) == 1 and myinput not in keywords:
        print "right,ok,done"
        myinput1 = myinput[1:]
    for otherchar in myinput[1:    ]:
        if otherchar not in alp + nums or myinput in keywords:
            print "invalid,need symbols ."
            break